The present invention relates to an improved plastic floor tile, and more particularly to a plastic floor tile, the lower face of which is formed with an internal stress-eliminating structure at four corners or margin portions so as to interrupt internal stress from reaching the corners or margin portions and prevent distortion thereof due to thermal change.
Conventional PVC floor tile, PVC color floor tile, PVC hollow floor tile, PVC asbestos floor tile and PVC soft pressed floor tile are more and more widely used due to their easy working, fine printed stripes, low price and slip-proof characters.
However between, these plastic floor tiles go through procedures of mixing, heating, pressing, lamination and pressing molding to form a laminated floor tile structure, and because PVC, filling, stabilizer, plasticizer, etc., are added to raw material with greatly different proportions for example, the proportion of filling is relatively large, and the affinity between these components are not in unison, therefore, when mixed, these components can be hardly uniformly mixed, and thus the floor tiles always are not uniformly composed of these components so that internal stress is created. Moreover, due to contractile character of PVC, the four corners and side edges of the plastic floor tile often suffer the internal stress caused by thermal change so that the four corners are often distorted or upward bent. As a result, after laid on the floor, the plastic floor tile is apt to contract and deform.
It is therefore tried by the inventor to research this problem and eliminate the aforesaid shortcomings. As shown in FIG. 1, because the components of the plastic floor tile are different from one another in molecular structure, therefore when under thermal change, the arrangement of the molecules of plastic floor tile is apt to vary to create inward internal stresses as indicated by arrows A, B, C, D, E, F, G, H in FIG. 1. Therefore, the floor tile is easy to inward contract Since the adhereing force of four corners to the floor appears to be relatively small in comparison with that of other portions of the floor tile, while the internal stress applied to four corners is larger than that of the other portions, therefore the distortion or bending of four corners of plastic floor tile is inevitable.